OUTLINE: Patients are stratified according to site of primary disease (hepatobiliary vs gastric vs pancreatic). Patients receive fluorouracil IV over 48 hours and hydroxyurea IV over 48 hours on days 1, 8, 22, and 29. Patients also receive interferon alfa subcutaneously (SC) on days 1, 3, and 5 and filgrastim (G-CSF) SC on days 3-6 of weeks 1, 2, 4, and 5. Treatment repeats every 6 weeks in the absence of disease progression or unacceptable toxicity.